It may not go along with the picture dictionary definition of "debt," but some things are more nuanced than a one-sentence definition. How about we just call those outstanding bonds, reserves, and dollars "national liabilities" instead of "national debt"? Would that make it easier to swallow? Because that's what they are - liabilities, in the accounting sense of the word. And those liabilities don't get extinguished by "repayment," they only get extinguished by running a budget surplus. (Another reason they should not be thought of as "debt.")
Debt service (interest) is used to effect monetary policy. That's the benefit, if you agree with the Fed's monetary policy.
This is an imperfect analogy, but I'm going to throw it out there anyway...
If you owned a giant apple orchard - the only one in the country - and apples (to you) were basically infinite, would a debt denominated in apples be a burden to you? No, you could merely pick all the apples you needed to satisfy your debts, with interest - and pay your bills, for that matter. Your ONLY concern with this situation is not spending so many apples that they become worthless. To that end, taxing some of those apples back might be a good idea.